In a method for detecting and measuring a target substance using a probe-label conjugate, wherein the probe specifically binds to the target substance and further the amount of the labels bound to the target substance via the probe is referred to as an indicator, the sensitivity is generally determined by the number of molecules of the probe and label. That is to say, since the number of molecules of the label which binds to one molecular of the probe is limited, the ratio thereof determines the sensitivity.
Thus, higher sensitivity with an improved reactivity has been achieved in such a manner that the probe itself is polymerized to produce a polymer thereby increasing the molecular weight thereof, and thus increasing the number of molecules of the label which binds to the polymer (Patent Literature 1). However, since it is not easy to control the polymerization of the probes, it has not been put to practical use.
Further, a label-probe complex having a high molecular weight and a large number of the labels, which is produced by covalently bonding one or more enzymatic labels and probes separately to a carrier such as polylysine and aminodextran, has been proposed (Patent Literature 2). However, although this technique increases reactivity, it also increases a reaction at a blank value, and thus does not provide higher sensitivity in detecting and measuring.
In addition, the following have been proposed: a label-probe complex in which one or more enzymatic labels are bound to a carrier such as polylysine and one or more probes are bound to the carrier through the labels on the carrier (Patent Literature 3); a water-soluble carrier-probe complex in which one or more probes are bound to a carrier such as dextran and one or more labels are bound to the carrier through the probes on the carrier (Patent Literature 4); a probe complex in which a hydrophilic intermediate is bound to a carrier and one or more probes and detection markers are bound to the intermediate (Patent Literature 5); and a blocked label-probe in which two or more carriers are bound to an enzymatic label to produce a complex and one or more probes are bound to the complex (Patent Literature 6).
However, the above-mentioned prior art involves a technical problem that a reaction at a blank value also increases while reactivity increases, and it has been difficult to obtain a highly sensitive and stable complex in the case of evaluating the reactivity as a signal-to-noise ratio. Further, when a carrier is first bound to the probe or label in the formation of a complex, it has been difficult to produce a desired complex with favorable reproducibility, resulting from multifunctionality of the carrier.